The present invention relates to switching facilities in network devices. More specifically, the invention relates to hardware switching of facilities in Synchronous Optical Network (SONET) cross-connect switches.
Redundant systems are a common mechanism for increasing the reliability of computer systems, network devices and networks. For example, in SONET cross-connect switches, 1-for-1 protection is often provided for incoming network facilities (or line cards). The redundant facilities are referred to as “working” and “protect” pairs. When a failure of performance degradation occurs on the working facility, the SONET specification states that the system should restore downstream traffic by switching to the protect facility within 50 msec of fault detection.
Current SONET implementations exist where software detects facility failures and restores the path by switching the output to the protect facility. Typically, there are software routines that monitor the facility path status, decide when to switch and perform the switch.
However, the software that monitors facility path status and effects a switch are executing on different system modules. Therefore, several inter-processor exchanges may be required before restoration of down-stream traffic occurs. This can place a difficult real-time burden on the software to meet the 50 msec constraint. Also, additional burdens may be present if the system is large and/or there are many simultaneous faults arriving at the system.
It would be beneficial to have new technologies that allow facility switching to occur rapidly (e.g., in 50 msec) even in the presence of many simultaneous network failures. Additionally, it would be beneficial if system software for facility switching is simplified and the bandwidth of inter-processor communications is reduced.